1. Field of the Invention
The present invention relates to a heating device for a bonding apparatus.
2. Prior Art
In conventional bonding apparatus heating devices which prevent the oxidation of lead frames, a guide groove which guides the lead frames is formed in a heating body, and a cover is fastened to the upper surface of the heating body so that the guide groove is covered as disclosed in, for example, Japanese Patent Application Publication (Kokoku) No. 2-54664.
In this device, however, a gap may be formed at the joining surfaces of the heating body and cover as a result of the heat of the heating body, warping of the cover or surface roughness of the joining surfaces, etc., so that air enters from the outside. As a result, the easily oxidizable lead frames which are made of copper or a copper alloy, etc. may be oxidized, so that the reliability of bonding drops.
One method that has been used in the past to prevent the entry of air from the joining surfaces of the heating body and cover is a method in which [a] grooves are formed in the heating body at the joining surfaces of the heating body (heating block main body) and cover (upper-lid heating block), [b] a crushable member consisting of a metal such as aluminum or a stainless steel pipe, etc., is installed in these grooves, [c] projections which engage with the grooves in the heating body are formed on the cover, and [d] the crushable member is crushed by these projections.
Since the crushable member consists of a metal, it has almost no elastic recovery force. As a result, once the member has been used, it cannot be used again. However, in such bonding apparatus heating devices, powdered metal from the lead frames falls into the guide grooves so that the guide grooves become soiled; accordingly, on a daily or weekly basis, the cover is removed and the guide groove areas are cleaned. In this case, since the crushable member cannot be reused, the crushable member must be replaced with a new crushable member. In other words, numerous spare crushable members must be kept on hand, and reproducibility cannot be obtained when these parts are replaced.
Furthermore, in order to insure a constant amount of crushing of the crushable member, it is important to obtain a high degree of precision in the external diameter of the crushable member, the depth of the grooves in the heating body and the height of the projections on the cover, etc. Moreover, since the projections on the cover are caused to engage with the grooves in the heating body, working is difficult. As a result, the device becomes more expensive. In addition, since the crushable member is heated to high temperatures by the heating body, the useful life of the crushable member is short. Furthermore, since the cover and crushable member have surface roughness, it is difficult to obtain a perfectly tight seal.